This invention relates to test apparatus for testing an automotive-type electronic ignition system and more particularly to test circuitry for detecting continuity, open circuit, lack of power and dynamic signal response faults in the various components within a transistor ignition system for a motor vehicle.
With the onset of electronic ignition systems for automobiles, power boats and small engine aircraft, mechanics face evermore severe problems in analyzing, diagnosing and isolating faults in such ignition systems. These new electronic systems have incorporated transistors and microelectronic components to perform functions previously accomplished mechanically or electromechanically. Most mechanics are not generally conversant with such state of the art solid-state electronic systems. Hence, most of them being schooled in prior art electromechanical ignition systems have great difficulty in dealing with the detailed aspects of electronic ignition systems. As ignition systems have become more electronically complex, standard test equipment for diagnostic testing of such systems has become more complex and expensive. However, this equipment which very often includes digital voltmeters, ohmmeters, oscilloscope and sweep pulse generators has not been designed specifically to test such transistor ignition systems. Moreover, the equipment puts out qualitative information which must be interpreted by the user. Very often an engineer instead of a technician or mechanic is required to operate such complex test equipment. Consequently, the expense and complexity of such test equipment has given rise to substantial questions as to the economic practicality of such equipment for the ordinary maintenance garage.
Simple test equipment, designed specifically for transistor ignition sytems, has heretofore not generally been available in the marketplace. In fact, only one such tester for electronic ignition systems has thusfar come to the marketplace. This unit is known as "UNI-TESTER ELECTRONIC IGNITION TESTER" provided by Chrysler Motors Corporation as described in instruction manual CM-923, and further identified by part number P/N 1-3500. As this Chrysler tester is a very recent development, very little is known about its structural configuration. This unit, however, is known to have a number of test circuits including a simulation circuit for performing shunt to ground and continuity tests. The Chrysler unit appears to be complex, having at least eight display lights and a six position function switch for controlling the operation of the tester. Additionally, this Chrysler tester does not appear to contain safety devices for preventing electrical damage to the ignition system under test or the testing apparatus itself other than circuit-breaker type components which open circuit after a finite period of time under short circuit conditions. These circuit-breaker type components require a finite period of time to reset and to render the tester operative again. The Chrysler safety devices are inconvenient as they render the unit inoperative for a fixed reset period of time. More importantly, they are undesirable as they subject the components within the tester and within the ignition system to short circuit conditions for a finite period of time during which such conditions may cause permanent damage to the circuitry of the tester or of the system being tested.
The major automobile manufacturers, American Motors, Chrysler, Ford and General Motors, have recently published shop manuals which teach methods for testing their transistor electronic ignition systems and show the type of equipment utilized. This equipment appears to be as discussed above. Moreover the coil, as taught by these manuals, is not tested as an isolated unit.
The coil has been tested by removing the coil's secondary wire from the distributor cap center tower and then positioning it to provide an air gap between that wire and the engine block. This procedure requires that a technician or mechanic provide a makeshift air gap between the center tower secondary wire of the coil and engine block ground. This test is very imprecise and does not provide a precise air gap test of the spark which would provide a substitute for spark plug operation. A consistant and reproduceable test of spark, i.e., the secondary output from the coil, is not easily obtained.
What is needed, therefore, is a very simple testing apparatus having a minimal number of controls and a minimal number of display components, wherein the testing apparatus is capable of testing each major component within a transistor ignition system to isolate a fault within that component apart from the other components within the ignition system. It is desirable to have such a test apparatus be "fool-proof" whereby the ignition system under test and the testing apparatus itself are protected from damage due to improper connection of test probes regardless of how finitely small the improper connection time period may be. It is important to remember that the transistor micro-component circuits of the ECU may be burned out very easily.
One object of the present invention is to provide electronic ignition system testing apparatus which is compact and portable, relatively inexpensive, and yet which is capable of performing those diagnostic tests needed to isolate the faults generally occurring in such ignition systems.
Another object is to provide a relatively simple testing apparatus amenable to be used in a testing procedure in itemized "cookbook" fashion providing "go", "no-go" output evaluations.
A further object is to provide such testing apparatus which incorporates a precise, separate spark indicator unit.
An even further object is to provide safety devices for preventing electrical damage to the ignition system under test or to the testing apparatus itself without rendering the testing apparatus inactive for any finite period of time.